The present applicant has found that cycloolefin random copolymers obtained by copolymerizing ethylene and cycloolefins such as tetracyclododecene are synthetic resins which are excellent in transparency and well-balanced among various properties such as heat resistance, thermal aging resistance, chemical resistance, solvent resistance, dielectric properties and rigidity, and also found that these copolymers exert excellent performance in a field of optical materials, e.g., optical memory discs and optical fibers. Based on these findings, the applicant has disclosed the cycloolefin random copolymers in Japanese Patent Laid-Open Publications No. 168708/1985, No. 98780/1986, No. 115912/1986, No. 115916/1986, No. 120816/1986 and No. 252407/1987. Further, it is also known that the copolymers described in these publications exert excellent performance in a field of structural materials.
However, there is yet room for improvement of the impact resistance in the cycloolefin copolymers, though they are excellent especially in the heat resistance and the rigidity. Moreover, even if the impact resistance is improved, the transparency inherent in the cycloolefin copolymers should be maintained.
The present applicant has also found that a composition comprising a cycloolefin random copolymer having a specific softening temperature (TMA) and a specific .alpha.-olefin elastomeric copolymer can be improved in the impact resistance without deteriorating other excellent properties such as heat resistance, thermal aging resistance and chemical resistance, and the present applicant has disclosed this composition in Japanese Patent Laid-Open Publication No. 163241/1989.
Further, the present applicant has also proposed in Japanese Patent Laid-Open Publication No. 167318/1990 a cycloolefin polymer composition improved in the impact resistance which comprises a reaction product obtained by reacting a specific cycloolefin random copolymer with a specific soft copolymer in the presence of an organic peroxide.
However, the cycloolefin polymer compositions proposed in Japanese Patent Laid-Open Publications No. 163241/1989 and No. 167318/1990 are not always satisfactory in the transparency and has yet room for improvement, though they are improved in the impact resistance.
The present applicant has further proposed resin compositions comprising cycloolefin random copolymers obtained by copolymerizing ethylene and cycloolefins (e.g., tetracyclododecene) and soft polymers (rubbers) in Japanese Patent Application No. 52971/1990.
These resin compositions are higher in the impact resistance than the cycloolefin random copolymers as they are, but they are desired to be much more improved in the impact strength. Further, the resin compositions are sometimes deteriorated in the transparency.
Moreover, in Japanese Patent Application No. 133822/1992, the present applicant has proposed a cycloolefin copolymer obtained by copolymerizing an .alpha.-olefin and a cycloolefin in the presence of a hydrocarbon elastomer having a polymerizable double bond.
This cycloolefin copolymer is also good in the impact resistance, but it is also desired to be more improved in the transparency.
Accordingly, the present inventors have further studied to solve such problems associated with the prior art techniques as described above. As a result, they have found that a cycloolefin polymer composition comprising two kinds of cycloolefin polymers having specific glass transition temperatures, specific refractive indexes and a specific difference in the refractive index therebetween, and a cycloolefin polymer composition obtained by radical reaction of the above composition in the presence of an organic peroxide and, if necessary, a radical polymerizable polyfunctional monomer are well-balanced among the impact resistance, the transparency and the heat resistance; and accomplished the present invention.
The present inventors have also found that a cycloolefin copolymer composition, which comprises a specific cycloolefin elastomer component [Aa] having a polymerizable double bond and a cycloolefin copolymer component [Ba] obtained by copolymerizing an .alpha.-olefin of two or more carbon atoms such as ethylene and a cycloolefin in the presence of the elastomer component [Aa] and which contains the component [Aa] in a specific amount wherein a difference between the refractive index n.sub.D (Aa) of the component [Aa] and the refractive index n.sub.D (Ba) of the component [Ba] is in a specific range, is excellent particularly in the transparency and the impact resistance; and accomplished the present invention.
The present inventors have further found that a cycloolefin copolymer composition, which comprises a specific cycloolefin elastomer component [A.alpha.] having substantially no polymerizable double bond and a cycloolefin elastomer [B.alpha.] obtained by copolymerizing an .alpha.-olefin of two or more carbon atoms such as ethylene and a cycloolefin in the presence of the elastomer component [A.alpha.] and which contains the component [A.alpha.] in a specific amount wherein a difference between the refractive index n.sub.D (A.alpha.) of the component [A.alpha.] and the refractive index n.sub.D (B.alpha.) of the component [B.alpha.] is in a specific range, is also excellent particularly in the transparency and the impact resistance; and accomplished the present invention.